This invention pertains to a telescoping straight edge or scale. In one of its more specific aspects, the invention relates to a telescoping scale where the edge of the scale forms a substantially straight edge throughout the telescoping range of the scale.
The conventional carpenter scale, which has been used in the past, is comprised of a plurality of small sections that are pivotally connected together to form an extendable scale. However, this extendable scale has a number of shortcomings that limit the usefulness of the scale. One of the major difficulties in using this type of scale is that when measuring in a horizontal plane, the weight of the cantilevered portion of the scale is often great enough to cause a portion of the scale to pivot in a direction away from the horizontal plane that is being measured. This problem becomes more significant as the scale becomes older and the force required to cause the sections to pivot is reduced. Thus, it can be very inconvenient to use this type of extendable scale when measuring in a generally horizontal plane.
Another shortcoming of this type of prior art extendable scale is that sudden or quick movements of the extended scale will frequently cause the scale to pivot around one of the points at which the sections are connected. The problem of having the extended scale close or pivot, when a sudden motion is applied to the scale, is very difficult to overcome without increasing the frictional engagement at the pivot points of the scale to a level that makes it very difficult to pivot the small sections during normal opening and folding of the scale.
Another drawback of the prior art extendable scale is that the scale does not present a very good straight edge when the scale is in the extended position. The pivot joints between the section of the scale are frequently slightly out of alignment so that the individual sections do not form a good straight edge when the scale is extended. In addition, even if the scale is constructed with a great deal of precision so that the scale formed a good straight edge when the scale is extended, use of the scale eventually causes the joints between the sections of the scale to become misaligned and, therefore, impair the straightness of the edge of the extended scale.